apart from when the drowsyness sets in
i was thinking more like making a jacket yourself. and dont use zed heater pads, no need for that, just use VAG ones im sure they are common as muck and normally have a 1-5 dial for them too. you could put a simple thermostat in if you felt like it too. It would be an option to just put them under the bottle to heat the compartment, you'd be surprised how hot those elements actually get if there isnt a seat of your arse soaking up the heat.